It is known that cyclic adenosine-3′,5′-monophosphate (cAMP) exhibits an important role of acting as an intracellular secondary messenger. The intracellular hydrolysis of cAMP to adenosine 5′-monophosphate (AMP) causes a number of inflammatory conditions, which include, but are not limited to, psoriasis, allergic rhinitis, shock, atopic dermatitis, Crohn's disease, adult respiratory distress syndrome (ARDS), eosinophilic granuloma, allergic conjunctivitis, osteoarthritis, and ulcerative colitis. Cyclic nucleotide phosphodiesterases (PDE), a biochemically and functionally, highly variable superfamily of the enzyme, is the most important factor in the control of cAMP (as well as of cGMP) levels. Eight distinct families with more than 15 gene products are currently recognized. Although PDE I, PDE II, PDE III, PDE IV, and PDE VII all use cAMP as a substrate, only the PDE IV and PDE VII types are highly selective for hydrolysis of cAMP. Accordingly, inhibitors of PDE, particularly the PDE IV inhibitors, such as rolipram or Ro-1724, are known as cAMP-enhancers. Immune cells contain PDE IV and PDE III, of which PDE IV is prevalent in human mononuclear cells. Thus, the inhibition of phosphodiesterase type IV has been a target for modulation and, accordingly, for therapeutic intervention in a range of disease processes.
The initial observation that xanthine derivatives, theophylline and caffeine inhibit the hydrolysis of cAMP led to the discovery of the required hydrolytic activity in the cyclic nucleotide phosphodiesterase (PDE) enzymes. More recently, distinct classes of PDE have been recognized, and their selective inhibition has led to improved drug therapy. Thus, it was recognized that inhibition of PDE IV could lead to inhibition of inflammatory mediator release and airway smooth muscle relaxation.
3-aryl-2-isoxazoline derivatives are known as anti-inflammatory agents and isoxazoline compounds are known as inhibitors of TNF release. However, there remains a need for new selective inhibitors of phosphodiesterase (PDE) type IV.